Hydraulic load indicator

ABSTRACT

This disclosure describes a hydraulic type load indicator for the measurement of large tensile forces. It comprises a load cell which is made up of two flat metal parts held together by screws. At the interface between the two parts is a flat neoprene circular diaphragm with molded circumferential &#39;&#39;&#39;&#39;O&#39;&#39;&#39;&#39; ring, a circular piston fits into a corresponding opening in the top plate and pressed on the diaphragm. There is a circular cavity under the diaphragm which is filled with liquid. Pressure on the piston causes downward movement of the diaphragm and compression of the liquid. The compression in the liquid is measured by a conventional Bourdon indicator element. A hook is attached to a yoke which slips over the two plates and pressed on the piston by means of a ball seated in a cavity in the center of the top of the piston. The principle novelty of this invention lies in the design of the diaphragm so as to provide linear readings of the pressure gauge with force supplied to the piston, and in the design of the system so that a very minimum volume of liquid can be used and thereby minimize the effect of temperature on the gauge reading due to the temperature expansion coefficient of the liquid. Another important feature includes the simplicity of the design, construction, and the assembly of the instrument.

United States Patent Franklin l l Feb. 18, 1975 HYDRAULIC LOAD INDKCATORtor for the measurement of large tensile forces. It [76] Inventor:Samuel Franklin, BOX 45181, comprises a load cell which is made up oftwo flat Tulsa Okla 74143 metal parts held together by screws. At theinterface l i between the two parts is a flat neoprene circular dial lFlledi l 1973 phragm with molded circumferential 0" ring. a cir- 21 A LN 39 ,933 cular piston fits into a correspondmg opening in the i I pp 03 top plate and pressed on the diaphragm. There is a circular cavityunder the diaphragm which is filled with Cl 73/141 1 7/208 liquid.Pressure on the piston causes downward move- [51] Int. Cl. Goll 1/02ment of the diaphragm and compression of the liquid. Field Of Search73/141 147 The compression in the liquid is measured by a conventionalBourdon indicator element. A hook is at- [56] References Cited tached toa yoke which slips over the two plates and UNITED STATES PATENTS pressedon the piston by means of a ball seated in 21 1,023,154 4/1912 Kenerson73/141 R x Cavity in the Center of the of Piston- 1.479,5.81 1/1924 Brry l77/203X The principle novelty of this invention lies in the219861933 6/1961 Grandstaffw 73/392 design of the diaphragm so as toprovide linear 311281937 4/1965 Bradley 73/141 R readings of thepressure gauge with force supplied to 0 11/1966 McDonough 73/141 R X thepiston, and in the design of the system so that a FOREIGN PATENTS ORAPPLICATIONS very minimum volume of liquid can be used and 171 1 5 11 199 Great Britain 77 20 thereby minimize the effect Of temperature on the435,623 10/1967 Switzerland t. 73/141 R gauge reading due to thetemperature expansion Primary Examiner-Charles A. Ruehl Attorney, Agent,or FirmI-lead & Johnson [57] ABSTRACT This disclosure describes ahydraulic type load indicacoefficient of the liquid. Another importantfeature includes the simplicity of the design, construction, and theassembly of the instrument.

6 Claims, 7 Drawing Figures PATENTEUFEBI 81915 $866,464

SHEEI 2 OF 2 HYDRAULIC LOAD INDICATOR BACKGROUND OF THE INVENTION Thisinvention lies in the field of force measuring and indicating devices.Still more particularly, it is in the field of tensile force measuringdevices of the hydraulic type in which the force to be measured istransmitted by a piston through a diaphragm to a confined liquid and thecompressive force in the liquid is indicated by a Bourdon type pressureelement.

In the prior art there are a number of examples of hydraulic load cellsof the general construction of this device; however, because of inferiordesign they are sub ject to errors which are avoided by the particulardesign of this invention. For example, some of these have insideseparation between the load cell and the Bourdon element, which becauseof the large volume of liquid and elasticity of the tubular connectioninvolve large piston travel, with corresponding variation in the area ofcontact between the piston and the diaphragm. Also, the large volume ofliquid subject to thermal expansion causes a corresponding change inarea of contact of the piston.

SUMMARY OF THE INVENTION It is a primary object of this invention toprovide an improved hydraulic load indicator in which the hydraulicfluid is of absolute minimum volume, in which the fluid is confined bymeans of a flat circular diaphragm with circumferential ring molded aspart of the diaphragm, and in which the force is applied through a balland socket connection to a piston which is adapted to press on thediaphragm and through the diaphragm to compress the liquid.

The indicator of the compression in the liquid is a Bourdon typepressure gauge of conventional design, that is mounted in very closeproximity to the load cell, so that there is a minimum of volume ofliquid between the diaphragm and the Bourdon tube.

Another feature is the use of a selected flow restriction in the liquidpath between the reservoir and the Bourdon tube. This utilizes a smalldiameter set screw which is inserted into a threaded portion of theliquid conduit, one side of one end of the screw is removed to leave oneor more complete turns of thread. When this modified set screw isthreaded into the opening there will be a very small clearance betweenthe remaining threads on the screw and the threads in the conduit whichserve as a constriction on the flow of liquid and provide a low pass,high out filtering action which makes the gauge insensitive to suddenshock forces.

BRIEF DESCRIPTION OF THE DRAWINGS These and other objects of thisinvention and a better understanding of the principles and the detailsof the invention will be evident from the following description taken inconjunction with the appended drawings in which:

FIG. I shows, in partial section, an overall view of the hydraulic loadindicator;

FIG. 2 shows a partial view of the load cell taken at right angles tothat of FIG. 1;

FIG. 3 shows a detail of the piston-diaphragmreservoir and sealing meansand the conduit leading to the Bourdon tube;

FIG. 3A indicates a possible condition of improper diaphragm contactwith the piston;

FIG. 4 is a detail of the constriction in the liquid flow channel;

FIG. 5 is a view of the Bourdon tube assembly;

FIG. 6 is a detail of the construction of the diaphragm.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawings,there is shown in FIG. 1 a general view of the instrument, which has twoprinciple parts; the load cell indicated generally by the numeral l0 andthe indicator shown generally by the numeral 12.

The force sensing portion of the device is confined to two plates ofmetal 24 and 26 which are accurately machined to fit together and sealthe space between them. As will be shown and described in detail in FIG.3, there is a space machined for a flat circular diaphragm 34 and forsealing the peripheral edges of the diaphragm. The upper plate 24 has acircular opening into which is fitted, with minimum clearance, acircular piston 32. which rests on the diaphragm 34. There is a shallowcircular cavity 36 machined out of the bottom plate 26 which is filledwith oil. This cavity, or reservoir, 36 is connected by a small diameterconduit 38 to one end 39 of the plate 26.

Attached to the end 39 of the plates 26 and 24 by means of screws, notshown, is a circular housing 40 inside of which is positioned a Bourdontube pressure measuring element with a pointer shaft, pointer andcircular scale, all of this being substantially conventional.

The two plates 24 and 26 are screwed securely together and a top plate14 is attached to the plates 24 and 26 by means of screws 20 and spacingblocks 28 and 30. An eye-bolt 16 is held in the top of the plate 14 bymeans of bolt 18, or in some similar manner. As shown also in FIG. 2,the hook 52 is swiveled at 54 in the bottom well of a rectangular yoke42. The yoke 42 includes an upper horizontal portion 85 which fitsfreely over the two plates 24 and 26. There is a drilled and threadedopening 46 in the top well of the yoke which holds a spherical ball 44by means of a threaded screw 48. The ball 44 fits into a sphericaldepression 50 in the center of the top of the circular piston 32.Consequently, when a tensile force is applied to the book 52, the yoke42 is pulled downward and communicates to the piston 32 through thespherical ball 44, the force which is applied to the hook.

FIG. 3 shows an enlarged view in cross section of a portion of thepiston 32, the diaphragm 34, and the cavity or reservoir 36. Thediaphragm has an O ring 62, molded onto the circumferential edge, asshown in FIG. 6. This molded O ring fits into a machined cavity 60, andserves to seal the pressure of the liquid in the reservoir 36. Theconduit 38 communicates between the reservoir 36, through the conduit 73in the housing 40, through a corresponding conduit 75 leading to theBourdon tube 76. By making the housing 40 of the gauge case thin, andmounting the Bourdon tube 76 in close proximity to the housing 40, andto the short conduit 38, there is an absolute minimum volume of liquidcontained in the pressure sensing and indicating system.

In the prior art it is well known that when there is excessive motion ofthe piston, due for example to expansion of the liquid below the piston,as shown in FIG. 3A, the the diaphragm will be lifted. Since the diaphragm is of substantial thickness, it will be partially arched andtherefore the contact between the liquid below the diaphragm and thepiston will be over an area which is slightly less than the actual areaof the piston, which is in contact with the diaphragm, when in thecondition shown in FIG. 3. This possible change in contact area which iscaused by expansion in the liquid is avoided in this device by makingthe liquid volume so small, that even though the liquid has some thermalexpansion, the resulting change in volume, due to the temperaturechange, will be insignificant so far as changing the effective area ofthe piston is concerned.

The depth of the cavity 36 is of the order of 0.010 to 0.0l inch and thetotal motion of the piston going from no load to full load is of theorder of a 0.002 to 0.005 inch.

In FIG. 3 the numeral 64 indicates the restriction, or constriction, inthe conduit 38 so as to avoid large sudden movements of liquid throughthe conduit on the application of shock force loads. This is shown ingreater detail in FIG. 4 where the conduit 38 is shown as being tappedout to provide threads 63. A short setscrew 64 is prepared by grindingoff a corner 65, of Se lected size, so that when the set screw 64 istightened into the threads 63, there will be a selected number ofcomplete threads 67 remaining. It is the very small clearance betweenthe tapped hole and the screw, over the several threads 67, whichprovide a tortuous path of small cross section for the liquid flow. Thisadds a short time constant to the indication of force, but it preventsthe application to the Bourdon tube a very sharp, short-time, pulses offorce and liquid pressure.

The conduit 73 in the housing 40 of the housing is provided with shallowcounter bores on each surface of the housing 40, into which are fittedO-rings 72 and 74, of such diameter that when the housing 40 is pressedagainst the end 39 of the plate 26 there will be no leakage out of theconduits 38, 73, or 75. Thus, the connection between the reservoir 36and the Bourdon tube 76 will be completely sealed, and will be ofminimum volume so as to minimize the temperature effect due to thevariation in density of the oil with temperature.

Referring to FIG. 5 the Bourdon tube indicated generally by the numeral66 is standard in every respect except that it is mounted to the backplate as shown. The Bourdon tube 76 is attached to a cylindrical hub 68with flange 69, which is attached to the back plate by means of screws70, as shown in FIG. 3. Because of the minimization of liquid volumethere has been found to be no need for temperature compensation of theoil by means of changes applied to the conventional Bourdon tube linkagesystem. This is shown as a link 77 attached to the end of the Bourdontube by pin 78 and attached in a sliding hinged manner, at point 79, tothe arm 80, which rotates about a pivot point 811. The arm 80 has a gearsector 82 cut on its circumferential surface which meshes with a smallpinion, not shown, which is mounted on the pointer shaft 83. This shaftsupports a long pointer which, as it rotates, indicates the angle ofrotation, or corresponding graduations of pressure. The operations ofadjusting the Bourdon tube, pointer, and scale is conventional in everyrespect and need not be discussed further at this time.

The liquid used in the hydraulic portion is a rather heavy oil, such asweight 40 motor oil, of good chemical antirust character. This heavy oilmakes quite simple to fill the cavities in the various plates 26, 40 and68 and assemble the three parts together in such a way that there is noloss ofliquid and no entry of air into the liquid space.

The diaphragm can be made of any compliant material although one whichis chemically insensitive to the hydraulic liquid must be chosen.Neoprene is a good material for this purpose. The diaphragmapproximately 1/1 6 inch thick, is adequate for the construction of thediaphragm.

While the invention has been described with a certain degree ofparticularity it is manifest that many changes may be made in thedetails of construction and the arrangement of components. It isunderstood that the invention is not to be limited to the specificembodiments set forth herein by way of exemplifying the invention butthe invention is to be limited only by the scope of the attached claimor claims, including the full range of equivalency to which each elementor step thereof is entitled.

What is claimed is:

I. A device for insertion between an upwardly and downwardly extendingline for measuring the tensile load comprising:

a plate having a hydraulic fluid filled cavity in the upper surfacethereof and a conduit opening communicating with the cavity;

a diaphragm sealably covering said cavity;

a cylindrical piston, the lower surface of which engages said diaphragm,the piston having an axially positioned spherical recess in the uppersurface thereof;

an upper line receiving means for securing an upwardly extending linethereto, said upper line receiving means being secured to said plate;yoke member having an upper horizontal portion extending above saidpiston, said yoke member being movable relative to said plate, the yokemember horizontal portion having a recess in the lower surface thereofin vertical alignment with said spherical recess in said piston;

a lower line receiving means adaptable to receive a downwardly extendingline, the lower line receiving means being attached to said yoke member;

a ball positioned in said recess in said yoke member horizontal portionand said cylindrical spherical recess in said piston, the tensile forceapplied by said lower line receiving means being applied by said ballagainst said piston; and

a hydraulic pressure actuated indicating instrument supported to saidplate and having communication with said conduit, the instrument beingcalibrated to reflect the tensile load applied between said upper andlower line receiving means.

2. A device for insertion between an upwardly and downwardly extendingline for measuring the tensile load according to claim I wherein saidplate includes:

an upper plate portion having a cylindrical opening therein slidablyreceiving said piston; and

a lower plate portion having said fluid filled cavity in the uppersurface thereof in register with said upper plate cylindrical openingand having said conduit opening therein, the peripheral surfaces of saiddiaphragm being sealably clamped between said upper and lower plateportions.

3. A device for insertion between an upwardly and downwardly extendingline for measuring the tensile load according to claim 2 including aring cavity in the upper surface of said lower plate portion concentricwith and surrounding said cavity and wherein said diaphragm is ofcircular contour and has an O-ring crosssection at its circumferencesealably received in ring cavity.

4. A device for insertion between an upwardly and downwardly extendingline for measuring the tensile load according to claim 1 wherein saidyoke member upper horizontal portion recess is in the form of a threadedopening and including a threaded screw received in said threadedopening, the lower end of the screw engaging said ball.

5. A device for insertion between an upwardly and downwardly extendingline for measuring the tensile load according to claim 1 wherein saidindicating instrument includes a Bourdon tube pressure indicating meanshaving communication with said conduit in said plate.

6. A device for insertion between an upwardly and downwardly extendingline for measuring the tensile load according to claim 5 including afluid flow restriction means in said conduit to isolate said Bourdontube from transient pressure peaks.

1. A device for insertion between an upwardly and downwardly extendingline for measuring the tensile load comprising: a plate having ahydraulic fluid filled cavity in the upper surface thereof and a conduitopening communicating with the cavity; a diaphragm sealably coveringsaid cavity; a cylindrical piston, the lower surface of which engagessaid diaphragm, the piston having an axially positioned spherical recessin the upper surface thereof; an upper line receiving means for securingan upwardly extending line thereto, said upper line receiving meansbeing secured to said plate; a yoke member having an upper horizontalportion extending above said piston, said yoke member being movablerelative to said plate, the yoke member horizontal portion having arecess in the lower surface thereof in vertical alignment with saidspherical recess in said piston; a lower line receiving means adaptableto receive a downwardly extending line, the lower line receiving meansbeing attached to said yoke member; a ball positioned in said recess insaid yoke member horizontal portion and said cylindrical sphericalrecess in said piston, the tensile force applied by said lower linereceiving means being applied by said ball against said piston; and ahydraulic pressure actuated indicating instrument supported to saidplate and having communication with said conduit, the instrument beingcalibrated to reflect the tensile load applied between said upper andlower line receiving means.
 2. A device for insertion between anupwardly and downwardly extending line for measuring the tensile loadaccording to claim 1 wherein said plate includes: an upper plate portionhaving a cylindrical opening therein slidably receiving said piston; anda lower plate portion having said fluid filled cavity in the uppersurface thereof in register with said upper plate cylindrical openingand having said conduit opening therein, the peripheral surfaces of saiddiaphragm being sealably clamped between said upper and lower plateportions.
 3. A device for insertion between an upwardly and downwardlyextending line for measuring the tensile load according to claim 2including a ring cavity in the upper surface of said lower plate portionconcentric with and surrounding said cavity and wherein said diaphragmis of circular contour and has an O-ring cross-section at itscircumference sealably received in ring cavity.
 4. A device forinsertion between an upwardly and downwardly extending line formeasuring the tensile load according to claim 1 wherein said yoke memberupper horizontal portion recess is in the form of a threaded opening andincluding a threaded screw received in said threaded opening, the lowerend of the screw engaging said ball.
 5. A device for insertion betweenan upwardly and downwardly extending line for measuring the tensile loadaccording to claim 1 wherein said indicating instrument includes aBourdon tube pressure indicating means having communication with saidconduit In said plate.
 6. A device for insertion between an upwardly anddownwardly extending line for measuring the tensile load according toclaim 5 including a fluid flow restriction means in said conduit toisolate said Bourdon tube from transient pressure peaks.